Failure-indicating nonexplosive insulators of the rod and hood type



Sept. 17, 1963 3,104,279

J. H. MEIER FAILURE-INDICATING NONEXPLOSIVE INSULATORS OF THE ROD AND HOOD TYPE Filed June 28, 1960 United States Patent m 3,104,279 FAlLURE-INDKIATING NUNEXPLOSIVE HNSULA= TGRS 6F THE R01) AND HUGE TYPE lean Henri Meier, Tarbes, France, assignor to Cie Generale dElectro-Ceramique, Paris, France, a company of France Filed June 28, 1960, Ser. No. 39,349 Claims priority, application France Sept. 1, 1959 '7 Claims. (Cl. l74182) The present invent-ion relates to improvements in suspended insulators of the hood and rod type, which are usually employed in chains for the insulation of high tension supply-lines.

These insulators usually comprise an insulating body constituted by a head sealed inside a metallic hood and fixed to a plate located below said hood.

It may happen under certain unfavorable circumstances that defective insulators are subjected to high-power arcing as a result of a perforation. Under these conditions, considerable energy can be generated under the hood, thereby resulting in the detachment of the insulator from the line.

The improvements in insulators of this type which form'the object of the present invention are intended to eliminate the causes of such an accident.

In accordance with the present invention, at least one portion of, reduced thickness is arranged in the insulator, so that in the event of excess voltage, the perforation of the insulator takes place in the zone which has thus been weakened, the location of said zone being chosen .so that an are which passes through the perforation remains as far as possible outside the space between the hood and the insulator in which the sealing material is located, or close to the external limit of said space.

The perforation and explosion phenomena are thus controlled by determining beforehand the point at which the perforation is liable to take place.

The description which follows below with reference to the accompanying drawings, which are given by way of example only and not in any sense by way of limitation, will make it quite clear how the invention may be carried into effect, the special features which are brought out either in the drawings or in the text being understood to form a part of the said invention.

FIG. 1 shows, half in cross-section and half in elevation, a form of construction of an improved insulator in accordance with the present invention.

FIG. 2 is a similar view showing a second form of construction.

The insulator of the hood and rod type illustrated in FIG. 1 essentially comprises an insulating body of ceramic material, for example, constituted by a head 1 comprising a bottom portion and an annular portion coupled to a portion having the shape of a dinner plate 2 usually provided with a number of fins 3. The head 1 is sealed, for example by means of a cement 6, inside a metallic hood 4 and a rod 5 is sealed in the interior of a housing la formed inside the head 1, by means of a sealing material 6' which is usually of cement. In order to ensure the adhesion of the cement on the external and internal cylindrical surfaces of the head 1, there is usually formed on said surfaces a roughened portion 7 and 8 comprising, for example, baked grains of ceramic material and an enamel.

In an insulator of this type, it will easily be understood that if, for any particular reason, a perforation of the insulator occurs in a zone located above the plane aa' which substantially corresponds to the lower edge of the hood, and that if the insulator which is thus damaged is subjected in addition to a power-arc, a considerable 3,104,279 Patented Sept. 17, 1963 energy can be generated in the chamber delimited by the hood. This energy results in fusion and volatilization of the material, thereby producing a high pressure and causing either the insulating head or the rod to explode.

In order that the perforation and explosion phenomenon should take place only below the plane aa' previously defined, the thickness of the coupling zone between the head 1 and the plate 2 is reduced. To this end, a groove 9 is formed in this zone so as to have a sufiicient thickness of the insulating material to enable the insulator to withstand the perforation voltage which it should normally be capable of ensuring but also of such thickness, however, that, for a higher voltage, the perforation necessarily takes place in this zone of reduced thickness.

The mechanical weakening created by the groove 9 also has the result of causing the plate 2 to be separated from the head 1 of the insulation unit, either at the time time of a perforation followed by arcing, or a result of a mechanical shock on the head of the rod 5. Any deterioration of the insulator can thus be clearly observed by a simple visual inspection and the damaged insulator can be rapidly replaced so as to avoid the serious drawbacks described above.

ln the form of construction of FIG. 2, the thickness of the base of the head of the insulation unit is substantially reduced at the level of its point of coupling with the plate 2, by virtue of a groove 13 which, in this example, is formed in the interior of the head and even located in the interior of the space filled with sealing cement, but close to the outer limit of said space.

Thus a perforation due to an abnormal voltage takes place invariably below the zone delimited by the line 11-11 which joins together the lower edge of the hood 4 and the small base of the frusto-conical head 11 of the rod 5, said frusto-conical head constituting the main part which ensures the mechanical strength of the rod anchorage.

In this form of construction, the sealing material is almost entirely subjected to compression on account of the frusto-conical shape and the relative position of the internal surfaces it} of the extremity of the hood and of the surface 11. The corresponding slope of the internal and external surfaces 12 and 10a of the insulating head 1 dispenses with the need for a roughened layer in order to ensure the adhesion of the cement on these ceramic surfaces.

This form of construction has various advantages. Accordingly, although the thinned port-ion of the dielectric l is comprised in the zone anchorage, a mechanical shock on the bolt 5 or an electric perforation both cause the separation of the plate 2 from the head 1 of the insulation unit in the coupling zone located outside the anchorage, which makes it wholly obvious that the insulator is damaged.

The conductivity of the cement is sufficient for this latter to behave in the thinned zone like a set of electrodes 6, 6 and the rounded profile of these pseudoelectrodes 6, 6' on each side of the dielectric increases the resistance, under the voltage of an electric shock, of the thinned portion 13 located in the vicinity and beneath this line b-b'.

Moreover, this conductivity of the cement which practically brings it to the potential of the elements 4, 5 with which it is in contact results in the fact that the thinned zone of the insulation unit is subjected to the voltage existing between the elements 4, 5 and not to a voltage which is ill-defined by the drop in potential along the insulating surfaces between the elements 4, 5 and the thinned zone in which the perforation is intended to take place. I

This gives rise to a reduced dispersionof the voltage at which the perforation actually takes place and, owing to the presence of the groove in the insulation unit, the

' effectiveness of control of the perforation zone is thereby improved.

Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made by way of example and that numerous changes in the details of construction and V the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafer claimed.

What is claimed is; V I

1. Insulator of the rod and hood-type comprising a metallic hood equipped with means for suspending same, a metallic rod equipped with suspension means, an insulating body having a head provided with a cavity open at one end, a plate and a connecting zone between the ing said cavity open and means for securing or fastening said metallic rod to the. interior of the cavity above 6. An insulator as claimed in claim 5, in which the insulating head has an inclined portion the internal and external surfaces of which are substantially parallel to the surface of the head of the rod, and the metallic hood has an inclined portion the internal surface of which is also substantially parallel to the said surfaces, all of these portions, the surfaces of which are parallel, being comprised substantially between two coaxial cones the generator lines of which are parallel and respectively pass through the small base and through the large base of the saidfrusto-conical head ofthe rod, the securing of the connection zone the thickness of which is reduced.

2. An insulator as claimed in claim 1, in which the connection zone between the insulating head and plate comprises at least one annular groove reducing its thickness to a point substantially smaller than any other part of said head.

3. An insulator as claimed in claim'1, in which theconnec tion'zone between the insulating head and plate comprises at least one recess reducing its thickness at the bottom of this; recess; tofa point substantially smaller than that-'of any otherpart'o f said head.

4. .An insulator'as'iclaimed'in claim 1,iin whichthe insulating head is secured by sealing material to the inf terior of the metallic hood and the portion of the con nection zone the thicknessof which is reduced is located beneath a horizontal. plane passing at the lower edge of the sealing material between the hood and the insulating 7 body.

5. An insulator as claimed in claim 1, in which the metallic rod comprises at its upper portion a frustoconical head the large base of which is upward and is secured by sealing material to the interior of the cavity of said insulating head and the portion of the connection zone the thickness of which is reduced is located below 'a slanted plane passing through the lower edge offthe hood and the small base ofthevsaid frusto-conical head.-

the insulating head around the rod on the one side, on the inside of the hoodon the other side being effected by means of sealing cement. i i

7. A failure-indicating explosion-resistant suspension insulator of the hood and rod type comprising; a metal hood having means for engaging a support and defining an annular open ended cavity oppositely disposed from said means for engaging a support; a metal rod having oppositely disposed ends and suspension engaging means on one of said ends; and an insulating body arranged intermediate said hood and rod, said insulating body having an annular head adapted to fit in said annular cavity of said hoodand being cemented therein, said head defining a'housing adapted to receivethe other of said ends of said metal rod which iscemented therein, said insulating body having a plate portion integral with said head and extending approximately normal thereto below and beyond the cavity end of said metal'hood, the thickness of material joining said head and plate approximately adjacent the cavity end of said hood being substantially less than the thickness of the remaining headmaterial cemented in said cavity, whereby failure of the insulator will tend to'occur in said material of less thickness between said hood and rod so that .the rupture of said platefrom said head will be visible to clearly indicate a V failure in said insulator, but said insulator being suitable for continued limited functioning.

References Cited in the file of this patent UNITED STATES PATENTS p Great Britain May 16, 1939 i 

1. INSULATOR OF THE ROD AND HOOD-TYPE COMPRISING A METALLIC HOOD EQUIPPED WITH MEANS FOR SUSPENDING SAME, A METALLIC ROD EQUIPPED WITH SUSPENSION MEANS, AN INSULATING BODY HAVING A HEAD PROVIDED WITH A CAVITY OPEN AT ONE END, A PLATE AND A CONNECTING ZONE BETWEEN THE HEAD AND THE PLATE, SAID ZONE HAVING AT LEAST AT ONE POINT A REDUCTION IN THICKNESS TO SUFFICIENTLY LESS THAN THE THICKNESS OF ALL OTHER PARTS OF SAID HEAD THAT A PERFORATION OCCURRING UNDER THE EFFECT OF A HIGH VOLTAGE NECESSARILY TAKES PLACE AT SAID POINT, MEANS FOR SECURING THE EXTERIOR OF THE SAID INSULATING HEAD TO THE INTERIOR OF THE SAID METALLIC HOOD ABOVE SAID CONNECTION ZONE AND LEAVING SAID CAVITY OPEN AND MEANS FOR SECURING OR FASTENING SAID METALLIC ROD TO THE INTERIOR OF THE CAVITY ABOVE THE CONNECTION ZONE THE THICKNESS OF WHICH IS REDUCED. 